Limit switch



Marh 2 1926.

' G. B. SCHEER LIMIT SWITCH Filed April 29, 1922 WITNESSYES: INVENTOR'pE Q. m Georye 5. 36/766,.

Patented Mar. 2, 1926.

"UNITED STATES PATENT OFFICE.

GEORGE B. SGHEER, OF BERKELEY, CALIFORNIA, ASSIGNOR T0 WESTINGHOUSEELEG-TRIO & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

' LIMIT SWITCH.

Application filed April 29, 1922. Serial No. 557,484.

To all whom it may concern:

Be it known that I, GEORGE B. SCHEER, a citizen of the United States,and a resident of Berkeley, in the countyofAlameda and State ofCalifornia, have invented a new and useful Improvement in LimitSwitches, of which the following is a speci-' fication. n My inventionrelates to electrical switching apparatus and it has particular relationto electric-motor control.

One object of my invention is to provide means for limiting the periodof opera- Gil tion of a motor.

Another object of my'invention is to provide an adjustable limit-switchthat shall be capable of-eifecting small movements of the apparatus tobe controlled, such as the edging rolls in a reversing steel mill.

Other objects of my invention will become apparentv from the followingspecification and the appended claims.

.My invention comprises a switch having an operating shaft arranged tobe controlled or rotated in accordance with certain movements of theoperating motor or mechanismthat is actuated thereby.

One or more movable switch members are actuated preferably, by means ofa cam which is operatively connected through an electromagnetic clutchto the operating shaft of the switch, The electromagnet is energizedsimultaneously with the. main motorcontrolling devices. The contactmembers are so arranged as to be capable of angular movementcorresponding to the movement of the cam, thereby affording adjustablemeans for retarding or for advancing the operation of themovable switchmember relative to therota-ry movement of the operating cam. A centeringspring 1s pro-' vided for returning thecam to its inoperative or offposition when the electromagnet becomes de-energized.

'Figure 1 of the drawing is a sectional view of apparatus embodying myinvention; .Fig. 2- is a plan view of aportion of the apparatusillustrated in-Fig.v 1; and

Figs. 3 and 4 illustrate theessential details of the centering springfor the operating cam.

I Referring particularly to;Fi 1, a mov-' able switch member 1 is carrieby a lever 2 and is arranged to. be actuted by a cam 3. Boththe cam 3and the lever 2 are supported by, and may be rotated about, a main 8 ofan electromagnet 9 and is arranged to control theaxial movement of theclutch member 6 by means of a hub portion 10 that is semi-cylindrical inform for convenience inassembling the clutch member 6 therewith. -Anyother convenient assembly may be employed; A compression spring 11 isdesigned to establish the necessary frictional engagement between clutchmembers 5 and 6 upon the energization of the electromagnet 9. Acentering spring 12, also illus trated in Figs. 3. and 4, normallymaintains the cam 3 in an operative position. A. torsional spring ofthis character is sufficiently familiar in design and function as not torequire detailed description. The various elements of the limit switchare contained within a casing 13, which provides suitable support forthese elements.

Referring to Fig. 2, it will be noted that movable contact member 1 ismounted upon and suitably insulated from the lever 2. Stationary contactmember 14 is also carried by the lever .2. The switch contact membersmay be of any desired character but I prefer to employ members capableof establishing a rolling contact under heavy sprmg pressure, such asthe familiar type that is illustrated in the drawing. Operation of themovable contact member 1 is effected by engagement of the roller switchmember 15 with the inclined surface of the cam 3. The switch members arecapable of any desired angular movement by means of the operating lever2.

It may be assumed, for example, that the shaft 4 of the limit switch isto be geared to a motor for operating rolls, such as in a steel mill.The motor may be started by means of a master switch (not shown) whichsimultaneously effects the energization of the electromagnet 9,, bymeans of an operating coil 16, and any suitable motor con-. trollerofelectromagnetio type (not shown). It may also be assumed .that thelever 2 has been set in any desired position, such as that illustratedin Fig. 2.

The engagement of clutch members 5 and 6 is effected by the closingmovement of the magnet armature 8. Rotary motion is transthe familiarno-voltage release coil of the main operating controller (not shown). orby any other well-known method, to effect interruption of the motorcontrol circuit.

The limit switch may, if preferred, be arranged with normally closedcontact members, the opening of which is effected by means of the cam 3.

A The interruption of the motor-control circuit results isde-energizing. the electromagnet 9, which returns the clutch member 6 toits normal or inoperative position, and also permits the centeringspring 12 to restore the cam 3 to its normal position. It is presumedthat the operator will return his master switch' or other controllingdevice to its inoperative ,position and reset the novoltage relay, afterwhich a second operation of the motor may be effected, as previouslydescribed.

It should be noted that the length .of time during which the motor ispermitted to operate depends upon the predetermined position or settingof the lever *2, which controls the angular movement of the cam 3 foradvancing or delaying each operation of the movable switch member 1. Theangular movement of the lever 2 is independent of the angular movementof rotation of the cam 3.

A reverse operation of the motor causes rotation of the cam 3 in theopposite direction and causes the-operation of the similarly disposedmovable contact member 21, mounted upon a lever 22, which is provided asillustrated in Fig. 2 for interrupting the motor-control circuit in thatdirection.

For the purposes of illustrating my invention, I have shown two sets ofswitch members, one set for each direction .of rotation of the motorsOther combinations may be arranged ahdother modifications may be madetosuit various operating requirements. I have described-a switch thatmay be 'used as a limit switch or that may be employed to accelerate orotherwise control a motor aswill be readily appreciated by thosefamiliar with the art. The advantages of my invention will be apparentto those employing unskilled labor, since, for any predetermined settingof, the limit switch,

the'control of the motor is entirely indev pendent of the skill of theoperator.

As there are many ways insiwhicha switch) of this character. may beemployedin. systoms of control, I have not deemed it necessarytoillustrate any particular system. The application of my invention willbe readily understood and various modifications therein may be madewithout departing from the spirit and scope thereof.

I claim as my invention:

1; A reversing limit switch comprising a rality of movable contactmembers and operating means therefor, comprising a single cam, anelectromagnetic clutch for rendering said meanselfective, a device forcontrolling the relative movements of'said contact members and saidoperating means and means i for restoring said contact members totheiroriginal positions independently of said operating means.

.3. A limit switch comprising a movable switch member, a cam foractuating the member, electromagnetic means for rendering the cameffective and means for predetermining the effective angular-movement ofsaid cam and for actuating said switch member independently of saidelectromagnetic means.

4. A limit switch comprising a cam operated switch member,electromagnetic means .for rendering said member effective, and

means for predetermining the angular movement of the cam and forcontrolling the total angular movement required for actuating saidswitch member and for controlling said switch member independently ofsaid electromagnetic means.

5. A limit switch comprising a movable switch member, a cam foractuating the member, electromagnetic means for rendering the cameffective and means for selectively controlling the effective angularmovement-of said cam to actuate the switch member and for actuating saidswitch member independently of said electromagnetic means.

' In testimony whereof, I have hereunto subscribed my name this 15th dayof April,

GEORGE B. SGHEER- Certificate of Correction.

1t hereby certified that in Letters Patent No. 1,575,010,- grented March2, 1926,

upon the application of- George B. Sc-heer, of Berkeley, California, foran improvementin' Limit Switches, an errorappears in the printedspecification requiring correction as follows: Page 2, line 87, claim 2,after-the word reversing insert the word limit; and-that-the saidLetters Patent should be read withthis correction therein that the samemay conform to the record of the case in the Patent Ofiice.

Signed and sealed this 13th day of April, A. D. 192 .6.

[m] M. J. MOORE,

Acting Uonmisezbmr ofPatvents;

